Process for the production of nitrates



Sept. 8, 1936. E, D, CRlTTENDEN 2,053,518

PROCESS FOR THE PRODUCTION OF NITRATES Filed May 8, 1929 5M/Ww INVENTOR guaivf @WITTE/yvan;

ATTORNEY Patented Sept. 8, 1936 PROCESS FOR THE PRODUCTION F NITRATES Eugene Dwight Crittenden, Syracuse, N. Y., as-

signor to Atmospheric Nitrogen Corporation, New York, N. Y., a corporation of New York Application May 8, 1929, Serial No. 361,414

7 Claims.

This invention relates to improvements in the making of nitrates from metals and has for its object the provision of an improved method of making nitrates of metals. More particularly the invention aims to provide an improved process lfor dissolving cobalt metal in nitric acid to produce a solution of cobalt nitrate of high concentration and purity.

Various procedures have heretofore been used `in making cobalt nitrate. In accordance with one of these procedures cobalt metal is dissolved in `an open dish by adding dilute nitric acid. When following this procedure, about 5.7 lbs. of 100% HNOS are required for the solution of one pound vof cobalt metal. This relatively large amount of nitric acid which is required in such a process may be partially accounted for by the vigorous Vevolution of nitrogen oxides during the reaction period and their escape from the materials in the dish. Another factor which may account for the large consumption of acid in this process is the diiculty in dissolving the last quantities of the cobalt metal.V

I have found that nitrates of metals of the type of c obalt, that is to say, metals which, in their reaction with concentrated nitric acid, are dissolved by an oxidizing action with liberation of nitrogenv oxide gases, may be made by reaction of the metal with nitric acid in a simple, efiicient manner. Examples of metals, the nitrates of -which may be made in accordance with my in- ,vention,.are cobalt, nickel, copper and silver.

I have found that cobalt nitrate, for example, may be made in a continuous manner and with greatly increased eciency over the heretofore customary methods. The process of my invention gives a high grade cobalt nitrate solution which may be made free from impurities present in cobalt metal'which are insoluble in nitric acid. I have found that cobalt metal may be dissolved in about one-half the quantity of nitric acid heretofore required for the solution of the metal to yield a cobalt nitrate solution having high concentration and purity and containing only a small 45 amountof free nitric acid. In contrast to the processes heretofore employed, I have found that.

the production of cobalt nitrate, comprises passing an aqueous solution of nitric acid into contact with a body of cobalt metal particles, which may be, for example, in the form of cobalt shot, and maintaining the vapors and gases which are evolvedby reaction of the nitric acid with the cobalt metal in contact with the body `of reacting cobalt metal particles. In its more specic embodiment, my invention comprises passing a stream of nitric acid into contact with an elongat- ..10 ed body of cobalt metal particlesand causing the evolved vapors and gases to pass in contact with the body of cobalt particles.

One example of a method of practicing this invention and an apparatus suitable therefor is ,15 as follows:

rLhe single figure of the drawing is a diagrammatic View partly in section of the apparatus.

The apparatus illustrated in the drawing comkprises a tower 5 of acid resisting material at the bottom of which is rigidly secured a foraminous screen 6 adapted to retain a charge of cobalt par ticles 'I within the tower 5. The bottom of the tower is formed of a flanged catch pot I5, the bottom portion of which is provided with a valved` drain I5. Screen 6 is secured betweenthe ilange of the catch pot and a flange I'I provided on the lower portion of tower 5.

A hopper 8 is adapted tointermittently charge the particles of cobalt into the tower through double valves 9 and I0. An outow pipe II is provided in the upper portion of thetower for vdrawing off the resultant solution from the tower. Movably mounted within the upper portion of the tower between the outflow pipe and the top of the charge of cobalt `particles is a foraminous screen I2. The screen I2 depends from a rod I3 which in turn extends upwardly through the top of the tower.

An acid feed line I4 enters the catch pot Iv5 below the screen 6 and extends upwardly, externally of the tower, to an appropriate distance abovethe desired liquid level within the tower.

Appropriate sealing devices are provided` on the overflow outlet and in the passage way for introducing the cobalt metal so that the evolved vapors and gases are conned to a great extent within the tower.

In the practice of the invention, the elongated tower 5 is lled with cobalt in divided form such as. shot, to any desired height below the outflow pipe II. Screen I2 is lowered into place between .the outow pipe I I and the top ofthe charge by means of the rod I3 extending throughl the top of the tower; Nitric acid is then introduced '55 through the acid feed line i4 and slowly rises through the cobalt charge and overflows through the outflow pipe ll. The flow of acid through the pipe I4 and the apparatus is then so regulated that the resultant liquid passing out of the outflow pipe Il contains a maximum quantity of cobalt nitrate and a minimum quantity of free acid. Y

The fresh acid, and consequently the most active acid, contacts first with the particles of cobalt which have already been acted upon and therefore contains the most resistantmaterial. There is an additional advantage in causing a current of reacting acid to rise in the tower. The evolved vapors and gases are repeatedly subjected to absorption by the solution and both the solution containing absorbed gases and vapors and any unabsorbed gas are simultaneously contacted with the newly exposed surfaces of metal in the upper portion of the tower. Fui thermore, the relatively large particles of material in the upper portion of the tower serve to retain the smaller and more completely dissolved particles and the insoluble impurities in the lower portion of the tower an-d prevent their being carried out through the overflow outlet with the solution leaving the tower.

The chemical reaction within the tower gradually depletes the charge of cobalt particles. From time to time as necessary, the screen l2 is raised and a fresh supply of cobalt particles introduced into the tower from the hopper 8 through the valves 9 and Il)V and the screen I2 again lowered into place. The cobalt metal in the lower portion of they tower is rapidly consumed by reaction with the fresh nitric acid introduced therein and is -replaced by a downward ow of the metal from the upper portion of the tower. Accordingly, there is maintained in the tower, a body of particles of-cobalt metal, the individual particles of which iiow countercurrent to the stream of nitric acid.

In the practiceof the invention, the screen I2 above the charge in the tower not only acts as a means to determine the depth of charge in the tower, butv it also prevents the larger particles of cobalt and solid impurities in the upper portion of the tower from being entrained in the flow of liquid and carried out of the tower through the outflow pipe H.

The foraminous screen 6 at the lower portion of the tower serves as a porous supporting means for the charge of cobalt in theV tower and permits the free entrance of the fresh acid. The lower screen also serves as a means of separating insoluble impurities, in the natureof silica and the like, from the charge by allowing the passage therethrough in one direction of lundissolved impurities and in the other direction of the inowing nitric acid. When'thefrimpurities accumulate in the lower Yportion of the catch pot they may be intermittently removed through drain I6 by opening the valve provided thereon.

The screens 6 and l2 maybe composed of any appropriate material suitable to withstand the difl'icult conditions to which they are exposed. Any appropriate Yacid resistant material is satisfactory. I have found it advantageous'to use nichrome metal cloth screens woven of nichrome wire of substantially 16 wires to the lineal inch.

It has been found advantageous when the apparatus is being used for the production of cobalt nitrate for use in the manufacture of a cobalt-aluminum catalyst for the oxidationr of ammonia, vto buildA the entire apparatus from aluminum or at least all the parts which come in contact with the acid or resultant solution. The aluminum is substantially acid proof and the slight quantity of aluminum nitrate formed in the resultant solution is not harmful to the finished catalyst.

When the apparatus is constructed in the main of aluminum, it has been found advantageous to make use largely of standard aluminum pipe and ttings. The threaded joints are screwed tight, and as a further precaution against leakage, they, may also be welded at the joint. A welded joint without the use of pipe threads is also found to be thoroughly satisfactory and reliable. Flanged joints are tted together very carefully and bolted tightly with asbestos or simil-ar inert packing between the contacting surfaces.

It is advantageous also, when slight amounts of valuminum are undesirable in the resultant solution, to construct the apparatus of chrome iron, glass, porcelain, enameled Ware or the like. This type of acid proof ware permits the production of cobalt nitrate without introducing into it any appreciable quantity of impurities from the action of the acid on the apparatus.

When standard commercial nitric acid of 38 YB. V(55% HNOS) is the source of the nitric acid employed in the process, it is diluted with water to a concentration of about 40% HNO3, which gives a high rate of solution, a reasonable acid consumption and a solution whose concentration of cobalt nitrate is very close to the saturation value (240 grams per liter).

The formationof cobalt nitrate in accordance with the example described above proceeds at a constant rate and delivers a uniform product. One of the main advantages'of carrying out the process in an elongated tower is the relatively l.high efliciency with respect to the amount of:

acid consumed. vThe tower reaction permits evolved vapors and gases to be absorbed in the resultant solution. This rather Vweak acid solution then-reacts readily with the newly exposed surfaces of cobalt metal with which it immediately comes into contact. Thus the obnoxious fumes are reduced to a minimum and the acid value of the nitric acid is efficiently utilized.

It is apparent to one skilled in the art that numerous changes may be made in the particu- -lar process and apparatus asdescribed above.

For example, the4 acid and metal may be introduced at the top of a tower, the nitrate solution removed from the bottom of the tower, and the residual gases removed from the top of the tower. The example described might be modified by introducing the acid at a mid portion of the tower, in which case the metal and acid would pass cocurrently through the lower portion of the tower and the nitric acid mist, vapors and gases would pass counter-current tothe descending metal; the residual gases being then removed from the top of the tower. The process may likewise be carried out at a pressure above atmospheric.

The process described above may likewise be modified by introducing oxygen into the tower as air or as a relatively pure oxygen gas. Nitric oxide which may be produced by reaction between nitric acid and cobalt metal is readily oxidized by means of free oxygen to form nitrogen tetroxide, which nitrogen tetroxide in yturn may react with the water content supplied to the tower to produce additional quantities of nitric acid which is available for reaction with the cobalt metal.

By employing oxygen in this 75 manner, the amount of nitric acid which is supplied to the tower to produce a given quantity of cobalt nitrate solution may be reduced.

I claim:

1. The process of making a solution of a nitrate of a metal of the type of cobalt which comprises contacting a stream of nitric acid with a body of said metal, and passing the evolved vapors and gases in intimate absorbing relationship with said stream of acid and passing the thus treated acid in contact with said metal.

2. 'Ihe process of making a solution of a nitrate of a metal ofthe type of cobalt which comprises contacting a stream of nitric acid with an elongated body of said metal in divided form and passing evolved vapors and gases with the stream of nitric acid in contact with newly exposed surfaces of said metal.

3. The process of making a solution of a nitrate of a metal of the type of cobalt which comprises contacting nitric acid with said metal in divided form in counter-current relationship and passing the evolved vapors and gases in cocurrent iiow and intimate contact with said acid while it is in contact with said metal.

4. The process of making a cobalt nitrate solution which comprises passing a stream of nitric acid in contact with a body of particles of metallic cobalt and maintaining the evolved vapors and gases in intimate contact with said stream of acid While the acid is in contact with said cobalt.

5. The process of making a cobalt nitrate solution which comprises contacting a stream of nitric acid with metallic cobalt, absorbing evolved gas in the resulting solution and passing the resulting solution in contact with newly exposed surfaces of cobalt.

6. The process of making a substantially saturated solution of cobalt nitrate by contacting nitric acid of a concentration of about 40% strength with particles of metallic cobalt the individual particles of metal and the nitric acid being passed in counter-current relationship with each other and maintaining the vapors and gases evolved by the chemical reaction in absorbing relationship with said acid.

7. The process of making a solution of a nitrate of a metal of the type of cobalt which comprises contacting a stream of nitric acid with a body of said metal and passing the vapors and gases evolved during substantially the entire progress of the reaction of the acid and metal in intimate absorbing contact with the acid and contacting the thus treated acid with said metal.

EUGENE lDWIGHT CRITTENDEN. 

